1. Field of the Invention
The present invention relates to an objective on the order of apochromat and, more particularly, to an objective for magnification of 10.times. to 15.times..
2. Description of the Prior Art
General objective designed on the order of apochromat and magnification of 10.times. to 15.times. comprise five or more lens components, thereby making the objectives rather heavy and requiring high manufacturing cost. In order to reduce both weight and manufacturing cost of objectives, it will be required to reduce the number of lens components and use low-priced glass having a low refractive index as material of each lens component.
When an objective system is designed with a small number of lens components which are made of glass having a low refractive index, however, spherical aberration is aggravated since it is required to enhance power of each lens surface and especially minimize radius of curvature on each surface.